gpio: gpio-xilinx: update on suspend and resume calls

Current AXI GPIO driver checking for interrupt data in suspend and
resume path and reporting as error in case of no interrupt connection.
As per AXI GPIO IP specification interrupt connection is optional,
driver logic is updated in suspend and resume calls by reporting
debug message and enable/disable clock in case of no connection.

Signed-off-by: Srinivas Neeli <srinivas.neeli@xilinx.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>